Silicon steels, ferrites, an amorphous alloys, a Fe-based nanocrystalline alloys, and the like are known as magnetic materials having high saturation magnetic flux density and excellent in alternating-current magnetic properties used for various transformers, reactors/choking coils, noise suppression parts, laser power sources, pulse power magnetic parts for accelerators, various motors, various generators, and the like.
The silicon steel sheet is made of an inexpensive material and has high magnetic flux density, but a problem of the silicon steel sheet is that its iron loss is large for high frequency applications. Another problem is that it is very difficult to process the silicon steel sheet to a thin sheet like an amorphous ribbon owing to the production process thereof and it is disadvantageous due to a large loss caused by a large eddy current loss. A problem of the ferrite material is its low saturation magnetic flux density and poor magnetic thermal properties. Another problem is that the ferrite, which is easily magnetically saturated, is not suitable for high power applications in which the operation magnetic flux density is high.
Further, a problem of a Co-base amorphous alloy is that it has a low saturation magnetic flux density of 1 T or less in the case of a practical material, resulting in thermal instability. For this reason, when it is used for high power applications, unfortunately, large parts are required and the iron loss increases due to a change over time. Moreover there is also a price problem because Co is expensive.
Further, a Fe-based amorphous soft magnetic alloy as described in Patent Document 1 (JP-A-05-140703 (paragraphs 0006 to 0010)) has good squareness and low coercive force and shows excellent soft magnetic properties. However, in the Fe-based amorphous alloy system, the physical upper limit of the saturation magnetic flux density is approximately 1.68 T. Furthermore, problems of the Fe-based amorphous alloy are that it has large magnetostriction and its properties deteriorate with stress and that it gives high noise in applications in which electric currents in the audio frequency band are superposed. In addition, in the conventional Fe-based amorphous soft magnetic alloys, when Fe is substantially replaced by other magnetic elements such as Co or Ni, the increase in the saturation magnetic flux density will be observed somewhat, but it is desired that the content (% by weight) of these elements be as low as possible in terms of the price. From these problems, soft magnetic materials having nanocrystals as described in Patent Document 2 (JP-A-01-156451 (from line 19 of the right upper column to line 6 of the lower right column on page 2)) are developed, and they are used for various applications.
Further, there has been disclosed a technique to produce a soft magnetic molded body having high magnetic permeability and high saturation magnetic flux density, in which an amorphous alloy having ultrafine crystals is first prepared and then annealed to produce nanocrystals, as described in Patent Document 3 (JP-A-2006-40906 (paragraphs 0040 to 0041)).    PATENT DOCUMENT 1: JP-A-05-140703 (paragraphs 0006 to 0010)    PATENT DOCUMENT 2: JP-A-01-156451 (from line 19 of the right upper column to line 6 of the lower right column on page 2)    PATENT DOCUMENT 3: JP-A-2006-40906 (paragraphs 0040 to 0041)